Transition-metal-free approaches to access N-heterocycles and valuable intermediates from aryldiazonium salts

Abstract

The discovery of novel and efficient synthetic methods to achieve valuable N-fused heterocycles has been an important research area in organic chemistry for several decades. Owing to the importance of N-fused heterocycles in medicinal chemistry, materials sciences, and organic synthesis, numerous efforts have been devoted to designing robust methods for the construction of N-heterocyclic molecules. Aryldiazonium salts are a privileged and readily accessible class of reagents/synthetic building blocks used in a diverse range of disciplines in chemical sciences. Aryldiazonium salts based on conventional C–C bond construction strategies have been well established. Alternatively, owing to their high electrophilic capacity, aryldiazonium salts have been broadly utilized in the efficient, atom-economic and rapid assembly of structurally unique nitrogen-containing heterocycles via the formation of C–N bonds in recent years. Herein, we review a diverse range of transition-metal-free synthetic methodologies using aryldiazonium salts as key synthetic precursors to afford highly useful N-heterocyclic frameworks over the past nine years (2015 to date). In addition, the application of these salts to prepare synthetically useful intermediates and precursors is also discussed. These N-heterocyclic motifs and intermediates are highly prevalent in a variety of natural products, agrochemicals and material applications.